when shifting into reverse it makes a clanking sound, and also when put into 4 low. dealer tells me nothing wrong with it.

The automatic transmission some times delays the application of power when starting from a stop. Other times, after sitting still for more than a minute with the engine on, like when parked at a project site, the transmission will sound and act strange when put into drive again. It sounds more like an 18-wheeler, with obvious changes in shift points and with a loss in power. The problem usually goes away after shutting down the truck for a few minutes, but returns often.